This application is directed to an improvement in the imaging system which is described in U.S. Pat. Nos. 4,399,209, 4,440,846 and 4,772,530 to Cycolor, Inc. These imaging systems employ a layer of photosensitive microcapsules. The microcapsules are prepared by microencapsulating a free radical polymerizable composition which contains an electron donating color precursor. Typically the image system assumes two forms. In one, the imaging system is a transfer system in which a support carrying a layer of photosensitive microcapsules is image-wise exposed to radiation and assembled with a developer sheet, e.g., a sheet containing a layer of a Lewis acid such as a phenolic resin. The assembly is subjected to pressure to rupture the microcapsules and the microcapsules image-wise leak their contents to the developer sheet where the color precursor is colored. In another embodiment, the imaging system is a self-contained imaging system in which the photosensitive microcapsules and the Lewis acid are carried on the surface of a common substrate in one layer or in juxtaposed layers. In a further embodiment of the invention, as described in U.S. application Ser. No. 08/570,658 now U.S. Pat. No. 5,783,353 and published International Application WO 95/34845, a layer containing photosensitive microcapsules and a developer material is interposed between two plastic films, at least one of which is transparent. Using a combination of an adhesive and a subbing layer, the films are permanently sealed to provide a film unit. This construction is advantageous because it prevents the chemical reactants in the imaging system from coming into contact with the user.
The imaging system is preferably a full color imaging system in which three different sets of microcapsules are used in combination and each set of microcapsules is sensitive to a distinct wavelength band. This full color system is described in U.S. Pat. No. 4,842,976. In accordance with one commercial manifestation of the imaging system, three sets of microcapsules respectively containing cyan, magenta and yellow color precursors are respectively sensitive to red, green and blue light are employed. In a further embodiment, these microcapsules are sensitized using a so-called "dye-borate photoinitiator" of the type described in U.S. Pat. No. 4,772,530 to Gottschalk. These photoinitiators, in one embodiment, are complexes of cationic cyanine dyes and a boranyl anion such as a triphenylbutylboranyl anion. For making photocopies and other applications employing visible light sources, imaging systems employing red-sensitive, blue-sensitive and green-sensitive microcapsules are desirable but one of the difficulties that is encountered in designing an imaging system with red, green and blue sensitivity is cross-talk. That is, the absorption spectra of the red and/or green and/or blue photoinitiators may overlap. In this case, it is important that in exposing the microcapsule to limit the amount of light which occurs in an overlapping region. Otherwise, the color quality of the reproduction will not be good. The art discloses a number of approaches that can be taken to mitigate this problem. However, with the proliferation of digital imaging systems, there are a host of applications in which red, green and blue sensitivity is not required. In particular printers can be designed which employ radiation sources which emit at wavelengths outside the visible spectrum, for example, in the infrared region. This presents an opportunity to minimize the problems associated with cross-talk since it is no longer necessary to restrict the sensitivity range of a photosensitive material to the visible region, the sensitivity of the imaging system can be extended into the infrared region at one end of the spectrum and optionally the ultraviolet region at the other end.